Magnetic system for dynamic loudspeakers



June 6, 1939- A. SAUERLAND 2,161,313

MAGNETIC SYSTEM FOR DYNAMIC LOUDSPEAKBRS Filed on. 12, 1936 INVENTOR AL FR0 SAUL-DLA ND ATTORNEY Patented June 6, 1939 UNITED STATES PATENT orrlca MAGNETIC SYSTEM FOR- DYNAMIC LOUDSPEAKERS tion of Germany Application October 12, 1936, Serial No. 105,215 In Germany November 4, 1935 1 Claim.

In permanent magnet systems for dynamic loudspeakers, in particular in systems wherein the magnetic steel consists of an alloy of high coercive force, considerable difflculties are en- 6 countered in the assembly of the system to provide a good and simple unit.

In the systems known in the prior art, the center pole piece and base plate as well as pole plate consist of soft iron. The magnet steel is arranged around the center pole piece between base plate and pole plate. The center pole is separately arranged in these constructions from the I baseplate. The center pole piece is either arranged movably in the base plate or it may rest I bluntly n the base plate. Due to the many impact points occurring in systems of this type the magnetic resistance assumes relatively large values in the magnetic circuit resulting in a reduction of the effective air gap induction.

Difficulties are further encountered in these constructions with respect tosimple assembly. As a rule, the assembly is accomplished in these types by providing specialtie-bolts disposed between the magnet steel and the center pole piece and engaging pole plate and base plate. The attachment of center pole piece to the base plate must be done by special means.

In place of the tie-bolts there may be used staybolts fixed to the magnet steel. It is, however, diflicult for a foundry to cast holes in magnet steel, particularly in aluminum-nickel steels with high coercive force. The pressing of the sleeves, required. for the stay-bolts, in the holes of the magnet steel easily causes additional tensions in the steel, resulting in a bursting of the latter since magnet steel is relatively coarsely crystal- 1 line and brittle.

These demerits are eliminated in accordance with the invention, in magnet systems where the magnet steel is developed as an exterior mantle pole, by making in one piece the center pole with the base plate. An impact point is avoided in this manner in the magnetic circuit and just exactly at a point where the greatest flux exists in the circuit. The base plate is suitably strengthened at the joining point with the. center pole for insuring a suflicient blending of crosssections and preventing magnetic saturation.

Particularly suitable has proved the casting of the center pole and the base plate in one piece. Dynamo cast steel has especially proved emcient and satisfactory.

This construction moreover insures the simplification of the assembly of the magnet system in that special eye lugs are provided protruding lattems.

erally from the center pole. These eye lugs are suitably cast as an integral part of the portion of center pole piece facing the air gap. The lugs are provided with threaded holes for receiving the bolts, preferably of non-magnetic material, that run through the pole plate. In this manner a simple and solid connection of the individual parts of the system is accomplished in the assembly. The usual bolt connections which engage the magnet steels or their interior are done away with, the result that no damage can be done to the magnet steels. Particularly in magnet systems, wherein the magnet steel consists of aluminum-nickel steels, the assembly is rendered considerably easier and waste is reduced by this arrangement.

Systems of this type may also be used to advantage for telescoping coil microphones and in all systems provided with a ring-like air gap whose yokes are made of permanent magnets.

Figs. 1 and ,2 show an embodiment by way of example of a magnetic system for permanent-dynamic loudspeakers in plan View and side view respectively. The center pole piece 1 forms an air gap 3 with pole plate 2. The exact spacing of air gap is insured by the centering ring 4. To the center pole I, preferably made of dynamo cast steel, there is directly cast the base plate 5. The center pole I increases conically towards base plate 5 whereby a sufflciently large crosssection is assured at the point of transition to base plate 5, preventing in reliable manner a saturation at these points. In given cases a strengthening of these points may also be accomplished in the manner that base plate 5 is strengthened exteriorly in line with the center pole. The part 6 is the magnet steel and is disposed between base plate 5 and pole plate 2. It preferably consists of a magnet steel of high coercive force such as is inherent in aluminumnickel steels.

On center pole I are provided towards the side facing airgap 3 several protruding eye lugs i, suitably cast as one piece with the center pole piece I. These eye lugs have internally threaded holes 8 for receiving bolts 9 of non-magnetic material. In the assembly of the system the bolts 9 are countersunk in the pole plate 2, thus insur ing a rigid adherence of the entire magnetic sys- The bolts 9 may be conveniently used at the same time for fastening the diaphragm supporting casing (not shown). The magnet steel 6 may consist of individual prismatic steels arranged in a circle or of a single cylindrical body.

What I, claim is:

A magnet system comprising an integrally cast base plate and center pole piece of soft steel, a pole plate of soft steel, a permanent magnet of high coercive force in the form of a cylindrical ring positioned between the upper surface of the base plate and the lower surface of the pole plate adjacent the outer peripheries of said plates, and means engaging an intermediate portion of the center pole piece and the pole plate for clamping the ring magnet between the above surfaces, said clamping means serving as the sole means for maintaining the magnet system in assembled position, said clamping means comprising a. plurality of internally threaded lugs extending outwardly from an intermediate portion of the center pole piece and integral therewith and a plurality of bolts, the headed portions of which are retained in countersunk portions on the upper surface of the pole plate and the threaded portions of which engage the internally threaded lugs.

ALFRED SAUERLAND. 

